JPS5933223B2 - Method and device for measuring alkali or acid concentration - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for measuring the alkali or acid concentration of a sample solution.

Specifically, the present invention uses an acidic or alkaline gas as a reagent, and measures the amount of heat generated when the gas dissolves in a sample solution and undergoes a neutralization reaction based on the temperature difference before and after the reaction, and calculates the alkali or acid concentration in the sample solution. The present invention relates to a method for introducing a sample gas substantially saturated with an aqueous medium into a reaction zone together with a sample solution, and an apparatus therefor. Conventionally, when measuring the alkali or acid concentration in a sample solution, a fixed amount of the sample solution is titrated with an acid or alkaline solution of a known concentration, and the amount of acid or alkaline solution of a known concentration consumed when the neutralization point is reached. Well-known titrators for quantifying the alkali or acid concentration of sample solutions have been put into practical use, but they have drawbacks such as the equipment being extremely complex and expensive, and the reagent solution having to be prepared to obtain a known concentration. .

A member of the present inventors previously proposed a continuous alkali or acid concentration measuring method and device that eliminates the above-mentioned drawbacks (
(See Japanese Patent No. 755438 and Japanese Patent Publication No. 16516/1983). However, it has been found that with this method, the temperature of the reaction zone decreases due to the heat of vaporization of the liquid that evaporates with the reagent gas, making it impossible to obtain accurate measured values.

This heat of vaporization varies depending on the temperature or gas flow rate, so
If the temperature of the outside air or the flow rate of the reagent gas fluctuates, the measured value will be further biased. For example, when carbon dioxide gas is used as the reagent and a 5% by weight aqueous solution of caustic soda is used as the sample solution, the influence of temperature and gas flow rate is as shown in Figures 3 and 4. If the temperature changes by 10°C, the measured value will change approximately. 6% fluctuation,
Furthermore, if the flow rate changes by 10%, the measured value will fluctuate by about 2%.

Therefore, as a result of further studies, it was discovered that if the reagent gas is moistened with an aqueous medium, evaporation of the liquid will not occur, so the effects of the above-mentioned outside temperature or reagent gas flow rate can be eliminated, and the present invention has been made. completed.

By the drawing showing an example of the apparatus used in the method of the present invention,
The method of the present invention will be explained in detail. FIG. 1 is a schematic longitudinal sectional front view of a continuous alkali or acid concentration measuring device.

In the figure, 1 is a sample solution, and 2 is a metering device for flowing an aqueous medium at a constant flow rate, and a metering pump or the like can be used. 8 is a constant pressure device for flowing a constant flow rate of reagent gas, and a pressure reducing valve 9
, a flow meter 10, etc.

Reference numeral 11 denotes a wetting section for substantially saturating and wetting the reagent gas with an aqueous medium, and a common air washing device equipped with a heater 12 is used.

The wet parts 11 may be connected in multiple stages. The sample solution and aqueous medium leaving the quantitative determination devices 1 and 2 are introduced into a temperature control section 3 in order to make each temperature the same. For the temperature control section 3, a commonly known heat exchanger can be used, such as a heat exchanger in which a coiled thin tube is arranged in a cylinder and a heat medium (for example, water) can be filled between the two. The sample solution leaving the temperature adjustment section 3 is introduced into the reaction section 6 via the pre-reaction temperature detection section 4.
Further, the aqueous medium is mixed with the reagent gas exiting the wet section 11 in the mixer 5, and then introduced into the reaction section 6. Saturated wetting of the reagent gas is preferably carried out by maintaining the temperature of the aqueous medium in the wetting section 11 at substantially the same temperature as the temperature of the sample solution in the pre-reaction temperature detection section 4. is the wet part 11
This is carried out by maintaining the temperature at about 2 to 5° C. higher than room temperature.

This treatment substantially saturates the reagent gas with the aqueous medium. The sample solution continuously introduced into the reaction section 6 is
First, it is mixed with a mixture of reagent gas and aqueous medium introduced from the nozzle 20 in the first chamber 19, and then introduced into the liquid in the second chamber 17 through the nozzle 18 in a gas-liquid mixed state.

During this time, a part of the reagent gas dissolves in the liquid, and a neutralization reaction takes place. At this time, heat of dissolution and heat of neutralization reaction are generated in the first chamber 19 and the second chamber 17, raising the temperature of the liquid phase. The solution and excess reagent gas after the reaction are stored in the third chamber 16.
After being separated into a gas phase and a liquid phase, it is discharged from the discharge pipe 15. The increased temperature of the liquid phase is measured by the post-reaction temperature detector 7 immersed in the liquid in the third chamber 16. In this way, the temperatures measured by the temperature detectors 4 and 7 before and after the sample solution comes into contact with the reagent gas are differentially taken out by the temperature difference measuring device 14.

FIG. 2 shows a schematic diagram of an example of the temperature measuring device 14, which measures with a combination of differential thermocouples 21 as shown in the figure, and has a scale 13 (FIG. 1) calibrated in advance with alkali or acid concentration. This allows you to directly read the alkali or acid concentration in the sample solution.

Note that it is desirable that the temperature adjustment section 3 and the reaction section 6 be housed in one case in order to further reduce the influence of ambient temperature.

Furthermore, in the apparatus shown in FIG. 1, the aqueous medium is temperature-adjusted, mixed with a reagent gas in the mixer 5, and introduced into the reaction section 6. It is also possible to connect the solution to the outlet conduit of the sample solution, mix it with the sample solution, adjust the temperature, and then introduce it into the reaction section 6.

Furthermore, the reaction section 6 is configured so that the sample solution, aqueous medium, and reagent gas are introduced from the bottom of a vertically long reaction tube having a gas-liquid separation section at the top, instead of the two-stage nozzle blowing cell shown in FIG. Various types of equipment can be used.

Sample solutions whose concentrations can be measured by the method of the present invention include sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium hydroxide,
Examples include alkaline solutions containing one or more of ammonia and organic bases, and acidic solutions containing one or more of hydrochloric acid, sulfuric acid, nitric acid, and organic acids.

Theoretically, the amount of reagent gas may be equal to or more than the equivalent amount, but in order to complete the reaction, the amount is desirably about 5 to 8 times the equivalent amount. Although it is desirable that the reagent gas be of high purity, it is also possible to use one diluted with an inert gas. However, if the purity is too low, the temperature difference before and after the reaction will be small and the measurement sensitivity will be reduced, so care must be taken when using a reagent gas with low purity. Examples of the reagent gas include acidic gases such as carbon dioxide gas, hydrogen chloride gas, sulfur dioxide gas, and nitrogen oxide gas, and alkaline gases such as ammonia and methylamine.

These reagent gases need to be appropriately selected depending on the target component whose concentration in the solution to be measured is to be measured. For example, when measuring only the concentration of sodium hydroxide in an alkaline aqueous solution system where sodium hydroxide and sodium carbonate coexist, it is preferable to use carbon dioxide, which is a weak acid gas, as the reagent gas, and use a strong acid gas such as hydrogen chloride. Then, it also reacts with sodium carbonate, making accurate measurement impossible. Water is usually used as the aqueous medium, but methanol,
It is also possible to use water containing a substance inert to the neutralization reaction, such as a water-soluble organic solvent such as ethanol or acetone, or a neutral salt such as common salt.

The amount of aqueous medium to be supplied should be about 0.05 times the volume of the sample solution or more, but if too much is used, the temperature difference before and after the reaction will become small and the measurement sensitivity will decrease, so the upper limit is 10
It is desirable to double the capacity.

It is preferably selected from a range of 0.1 to 3 times the volume.
There is no problem with the supply temperature of the sample solution, the aqueous medium, and the reagent gas as long as the neutralization reaction occurs quickly, but in consideration of ease of temperature control, it is preferable that the supply temperature be around room temperature. Furthermore, if there is a difference in the supply temperatures of these, the temperature difference before and after the reaction becomes small, which may reduce measurement sensitivity, so it is preferable that the temperatures of the sample solution, aqueous medium, and reagent gas be the same.

A thermocouple element is usually used to detect temperature, but a thermistor element or a resistance thermometer can also be used.

Furthermore, as a means of obtaining a temperature difference, it is preferable to use differential thermocouples as shown in Figs. 1 and 2, as this can simplify the device the most, but other methods, such as increasing the potential difference between each thermocouple, are preferable. After measuring the width, you can also use a subtractor to get the temperature difference. As the thermocouple, known thermocouples such as copper-constantan, chromel-alumel, and iron-constantan can be used, but copper-constantan is advantageous because of its large thermoelectromotive force. As detailed above, in the method of the present invention, by introducing the reagent gas into the reaction zone after wetting it,
Since a temperature drop in the reaction zone due to heat of vaporization can be prevented, accurate measurement values can be obtained without being affected by outside temperature and reagent gas flow rate fluctuations.

In addition, when an aqueous medium is introduced into the reaction zone in addition to the sample solution and reagent gas, clogging of the reaction tube due to reaction products in the sample solution can be prevented, allowing accurate and continuous measurement of the alkali or acid concentration of the sample solution. can do. In addition, it has various advantages, such as being cheaper than the well-known tie radar, simple to operate, and requiring no preparation of reagents, and is particularly suitable for continuous analysis methods.

Further, if the detected value obtained by the method of the present invention is used to open and close a valve for adjusting the alkali or acid concentration, the concentration can be automatically maintained within a specific range at all times.

Furthermore, the method of the present invention is widely applicable not only to the above-mentioned neutralization reaction, but also to the measurement of other exothermic or endothermic reactions, especially reactions between gases and solutions or liquids. Next, the present invention will be specifically explained with reference to Examples.

Example 1 Water in a circulating alkaline aqueous solution (an aqueous solution containing 2 to 3% by weight of NaOH, 35% by weight of Na2cO, and 5% by weight of NaCl) used to absorb and remove phosgene contained in the exhaust gas of the phosgenation reaction to make it non-polluting. The concentration of sodium oxide was measured continuously using water as the aqueous medium and carbon dioxide as the reagent gas.

The apparatus used for the measurement has the structure shown in FIG.
5mmL1 thermocouple (Figure 2) is 0.211φ copper-0.0
57!171Lφ constantan 5 pairs, the indicator [Fig. 1 14] is a 2 m voltmeter, and the scale [Fig. It is measured and calibrated to directly display the concentration.

Sample solution and water flow rates are 5d/Rk and 1d, respectively.
/? The flow rate of carbon dioxide gas (approximately 99%) was measured at 500 m1/-. The measurement error was only ±2% (relative error) of the NaOH concentration, and the accuracy was extremely high.

In addition, although the supply of the circulating alkaline aqueous solution was stopped for about 1 hour each time after 1FH1I, there were no problems such as precipitation of reaction products or clogging of the reaction tube due to caking.

For comparison, the concentration of NaOH was measured in exactly the same manner as in Example 1, except that the wet part 11 was not used.

The measurement error is affected by room temperature and the flow rate of carbon dioxide, and NaO
The H concentration varied between ±701) (relative error).

[Brief explanation of the drawing]

Figure 1 is a schematic vertical cross-sectional front view of an example of a continuous measuring device used in the present invention, Figure 2 is a schematic illustration of the temperature detection section in Figure 1, and Figures 3 and 4 are temperature, reagent gas flow rate, and measurement. FIG. 3 is a diagram showing the relationship between errors. 1, 2...Quantitative device, 8...Constant pressure device, 3...Temperature adjustment section, 6...Reaction section,
18, 20... Nozzle, 4... Pre-reaction temperature detector, 7... Post-reaction temperature detector, 15.
...Discharge port, 21...Differential thermocouple, 14
...Temperature difference measuring device, 13...Scale.

Claims (1)

[Claims] 1. A continuous method in which an acidic or alkaline reagent gas and a sample solution are continuously supplied to a reaction zone, and the alkali or acid concentration of the sample solution is measured from the temperature difference between the sample solution before and after the reaction zone. A method for measuring alkali or acid concentration of a sample solution, which comprises introducing a reagent gas substantially saturated with an aqueous medium into a reaction zone together with the sample solution. 2. An alkali or acid concentration reactor equipped with a flow reactor, a sample solution supply conduit and a reagent gas supply conduit connected to the reactor, and means for detecting the temperature difference between the sample solution before and after the reaction in the reactor. The measuring device is characterized in that the reagent gas supply conduit has a gas-liquid contact means in the middle thereof, and the reagent gas is configured to flow into the reactor after coming into contact with an aqueous medium in the gas-liquid contact means. A device that does this.